1. Field of the Invention
This invention relates to an intake-negative-pressure-increasing apparatus for an engine.
2. Description of the Related Art
Japanese Unexamined Patent Publication No. 11-342840 discloses an engine comprising a bypass passage bypassing a throttle valve and an idle speed control valve (hereinafter referred to as the ISC valve) arranged in the bypass passage. The flow rate of the air flowing in the bypass passage can be controlled by controlling the opening degree of the ISC valve. In the engine described in Japanese Unexamined Patent Publication No. 11-342840, in the case where an idling operation is required, the throttle valve is closed while at the same time the ISC valve is opened, and further, by controlling the opening degree of the ISC valve, the intake air amount (the amount of the air introduced into the combustion chamber) is controlled thereby to control the engine speed during an idling operation.
Also, in the engine described in Japanese Unexamined Patent Publication No. 11-342840, a negative pressure is generated by the air flowing through the bypass passage and introduced into a brake booster. Thus, a negative pressure corresponding to the flow rate of the air passing through the bypass passage is generated. In other words, by controlling the opening degree of the ISC valve, the intake air amount and the magnitude of the negative pressure generated by the air flowing through the bypass passage are controlled.